The present invention relates to a semiconductor temperature sensor.
A conventional semiconductor temperature sensor is described. FIG. 3 is a circuit diagram illustrating the conventional semiconductor temperature sensor.
PNP bipolar transistors (PNPs) 202-204 are in Darlington connection. A constant current is supplied to respective emitters of the PNPs 202-204. Based on the constant current and the temperature, an output voltage which is a sum of base-emitter voltage VBE of the PNPs 202-204 is output (see, for example, JP 3128013 B).
Next, a structure in cross-section of the PNPs 202-204 of the conventional semiconductor temperature sensor is described. FIG. 4 is a cross-sectional view illustrating a PNP of a semiconductor temperature sensor.
The PNPs 202-204 have a P− silicon substrate 102, an N diffusion layer 103, a P+ diffusion layer 104, an N+ diffusion layer 105, a P+ diffusion layer 106, an intermediate insulating layer 107, a collector electrode 108, an emitter electrode 109, and a base electrode 110. The N diffusion layer 103 and the N+ diffusion layer 105 form a base region, the P+ diffusion layer 104 forms an emitter region, and the P− silicon substrate 102 and the P+ diffusion layer 106 form a collector region.
However, in the conventional semiconductor temperature sensor, as the temperature increases, a leakage current is generated at a junction between the N diffusion layer 103 and the P− silicon substrate 102. More specifically, the leakage current is generated at bases of the PNPs 203 and 204 (leakage current between the bases and collectors of the PNPs 203 and 204). Because the leakage current is a part of constant current passing through the emitters of the PNPs 202 and 203, it follows that an emitter current of the PNPs 202 and 203 decreases correspondingly. This results in correspondingly lower base-emitter voltage VBE of the PNPs 202 and 203, and thus, linearity of an output voltage with respect to the temperature becomes worse.